An object with a mass of 12 kg12kg is on a surface with a kinetic friction coefficient of 1 1. How much force is necessary to accelerate the object horizontally at 14 m/s^214ms2?

1 Answer
Apr 20, 2016

290N["forward"]290N[forward]

Explanation:

For this problem it is important to note that there are two forces acting on the object in the xx direction, the applied and friction forces.

Start by listing out the given and required values.

m=12kgcolor(white)(i)color(teal),color(white)(i)mu_k=1color(white)(i)color(teal),color(white)(i)a=14m/s^2color(white)(i)color(teal),color(white)(i)F_"app"=?m=12kgi,iμk=1i,ia=14ms2i,iFapp=?

A free-body diagram can represent the situation as:

![http://www.physicsclassroom.com/class/newtlaws/Lesson-2/Drawing-Free-Body-Diagrams](useruploads.socratic.org)

In this case, set the positive directions to be forward and down.

Using F_("net",y)=ma_yFnet,y=may, add the forces in the yy direction.

F_("net",y)=ma_yFnet,y=may

F_N+Fg=ma_yFN+Fg=may

Since the object does not accelerate vertically, the acceleration in the yy direction is 0m/s^20ms2.

F_N+Fg=m(0m/s^2)FN+Fg=m(0ms2)

F_N+Fg=0NFN+Fg=0N

F_N=-FgFN=Fg

color(blue)(|bar(ul(color(white)(a/a)color(black)(F_N=-mg)color(white)(a/a)|)))

After adding the forces in the y direction, do the same for the forces in the x direction. Rearrange for F_"app" to find the force needed to accelerate the object horizontally.

F_("net",x)=ma_x

F_"app"+F_(f,k)=ma_x

F_"app"=ma_x-F_(f,k)

F_"app"=ma_x-mu_kF_N

F_"app"=ma_x-mu_k(color(blue)(-mg))

F_"app"=ma_x+mu_kmg

Substitute your known values.

F_"app"=(12kg)(14m/s^2)+(1)(12kg)(9.81m/s^2)

F_"app"=285.72N

F_"app"~~color(green)(|bar(ul(color(white)(a/a)290Ncolor(white)(a/a)|)))